1. Field of the Invention
The present invention relates to a magnetic tape and to a method of manufacturing the same. More particularly, it relates to a magnetic tape affording both good electromagnetic characteristics and good recording retention property, and to a method of manufacturing the same.
The present invention further relates to a magnetic recording device comprising the above magnetic tape.
2. Discussion of the Background
As the quantity of recorded information has increased, ever higher recording densities have been demanded of magnetic recording media. Accordingly, to achieve high-density recording, the practice of increasing the fill rate of the magnetic layer by using microparticulate magnetic powders has been widely employed.
Conventionally, primarily ferromagnetic metal magnetic particles have come to be employed in the magnetic layer of magnetic recording media for high-density recording. However, a limit has begun to appear in the improvement of ferromagnetic metal magnetic particles to achieve higher density recording. By contrast, the coercive force of hexagonal ferrite magnetic particles is great enough for them to be used in permanent magnetic materials. Their magnetic anisotropy, which is the basis of this coercive force, derives from their crystalline structure. Thus, it is possible to maintain the coercive force even when the particles are reduced in size. Further, magnetic recording media with magnetic layers in which hexagonal ferrite magnetic particles are employed can exhibit high-density characteristics based on the vertical component. Thus, hexagonal ferrite magnetic particles are a ferromagnetic magnetic material that is suited to achieving higher densities.
However, since hexagonal ferrite magnetic materials are tabular in form, in contrast to ferromagnetic magnetic particles, which are acicular in form, and since they have an easily magnetized axis in a direction perpendicular to the tabular surface thereof, they tend to undergo stacking (a state where the magnetic particles aggregate like the beads of an abacus). When the magnetic particles aggregate, a state similar to that of coarse particles being present in the magnetic layer is created, even with microparticles. The noise increases, causing the SNR to drop. As a countermeasure, attempts have been made to prevent aggregation (stacking) of the particles by increasing the dispersion of hexagonal ferrite. In this context, reference can be made to Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-178916 (Reference 1), Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-283218 (Reference 2), Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-144615 (Reference 3), Japanese Unexamined Patent Publication (KOKAI) No. 2002-298333 (Reference 4) or English language family members US 2003/049490A1 and U.S. Pat. No. 6,689,455 B2, and Japanese Unexamined Patent Publication (KOKAI) No. 2009-099240 (Reference 5) or English language family member US 2009/098414 A1, and Japanese Unexamined Patent Publication (KOKAI) No. 2002-373413 (Reference 6), which are expressly incorporated herein by reference in their entirety.
Further, when the size of the magnetic particles is reduced, the energy maintaining the magnetic particles in the direction of magnetization (magnetic anisotropy energy) tends to be difficult to overcome thermal energy, and so-called thermal fluctuation ends up causing recording retention property to drop. Attempts have been to resolve this, primarily by increasing the thermal stability of the magnetic powder. In this context, reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2001-297423 (Reference 7) or English language family members US 2002/018915 A1 and U.S. Pat. No. 6,521,361 B2, Japanese Unexamined Patent Publication (KOKAI) No. 2003-059026 (Reference 8) or English language family members US 2003/113585 A1 and U.S. Pat. No. 6,773,788 B2, Japanese Unexamined Patent Publication (KOKAI) No. 2002-260211 (Reference 9) or English language family members US 2002/164504 A1 and U.S. Pat. No. 6,620,499 B2, Japanese Unexamined Patent Publication (KOKAI) No. 2002-260212 (Reference 10), Japanese Unexamined Patent Publication (KOKAI) No. 2002-074640 (Reference 11) or English language family members US 2002/045067 A1 and U.S. Pat. No. 6,727,009 B2, and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-236404 (Reference 12), which are expressly incorporated herein by reference in their entirety.